I am Diamond with Sixt, and never had this problem before, but there is always a first time. Renting in SPU, the Sixt office REQUIRED me to sign a document since I was not getting their protection plan saying that I understood that I was responsible for ALL damage, and even if I have CC coverage, I had to front all monies first. Fine, I guess, a bit of a hard sell, but ok. Then next, they take my credit card and tell me it declined. I asked how much they were trying to charge, and I am told its 40,000HRK. This is $6735USD, that I am told is a 'deposit'. They try another of my cards, which declines of course (Even though I have more than enough available credit, I am sure they are wondering what this random charge is from Croatia for such a huge amount), and the agent says he cannot rent me a car unless he can charge at least 30,000HRK, "but this is the minimum". Finally, my corp Amex took the charge without me having to call them, but in the end this is a station I would most definitely avoid in the future. If you need that much of a deposit for a car (especially for a top tier member with a history of no damage), maybe you shouldn't be in the business.